1. Field of the Invention
The invention relates to a memory device whose memory information is stored in fuse memory cells. Furthermore, the invention relates to a method for operating such a memory device and a use of the memory device.
2. Description of the Related Art
So-called fuse memory cells are increasingly being used in integrated circuits, particularly in semiconductor memories, such as dynamic random access memories or DRAMs for example. A fuse memory cell essentially comprises a metal-metal connection having a low contact resistance, which can be interrupted after the actual production process, whereby the contact resistance of the fuse memory cell is increased. The fuse memory cell can thus assume the programming states “conducting” and “non-conducting”, that is to say that it represents either a logic 1 or a logic 0.
The metal-metal connection of a fuse memory cell is interrupted as required either by the application of a current or by the action of a laser beam. Depending on the method by means of which their metal-metal connections can be interrupted, fuse memory cells are referred to as electrical fuse memory cells or as laser fuse memory cells.
One useful application of fuse memory cells in integrated circuits relates to the storage of secret keys for cryptography purposes and of data which are required for system configuration. Since the fuse memory cells used for this purpose are generally electrical fuse memory cells, for a corresponding programming, the respective fuse connections have to be interrupted by means of a fusing voltage that is high enough to melt the fuse resistance. For this purpose, a programming unit is provided, which is arranged on the same chip as the fuse memory cells and which has a terminal to which an external fusing voltage can be applied. After the programming has been concluded, 0 V is applied to the said terminal again.